Category.php

<?php

namespace Acme\DemoBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Mablae\WirGehenMitBundle\Entity\Category
 *
 * @ORM\Table(name="feedbackcategory")
 * @ORM\Entity(repositoryClass="Mablae\WirGehenMitBundle\Entity\CategoryRepository")
 */
class Category
{
   /**
    *
    * @ORM\Id
    * @ORM\Column(type="integer")
    * @ORM\GeneratedValue(strategy="AUTO")
    */
    protected $id;

    /**
     * @ORM\Column(name="name",type="string")
     */
    protected $name;

    /**
     * @ORM\ManyToOne(targetEntity="Category")
     */
    protected $parent;

    /**
     * Get id
     *
     * @return integer
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set name
     *
     * @param string $name
     */
    public function setName($name)
    {
        $this->name = $name;
    }

    /**
     * Get name
     *
     * @return string
     */
    public function getName()
    {
        return $this->name;
    }

    /**
     * Set parent
     *
     * @param Category $parent
     */
    public function setParent( Category $parent )
    {
        $this->parent = $parent;
    }

    /**
     * Get parent
     *
     * @return Category
     */
    public function getParent()
    {
        return $this->parent;
    }

    public function __toString()
    {
        return $this->name;
    }

    public function isTopLevel()
    {
        return $this->getParent() == null ? true : false;
    }

    public function getCategoryTypeTitle()
    {
        return array('isTopLevel' => $this->isTopLevel(), 'label' => $this->getName());
    }
}

CategoryType.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Acme\DemoBundle\Form\Type;

use Doctrine\Common\Persistence\ObjectManager;
use Symfony\Component\Form\AbstractType;
use Symfony\Bridge\Doctrine\Form\ChoiceList\ORMQueryBuilderLoader;

class CategoryType extends AbstractType
{


    public function getName()
    {
        return 'category';
    }

    public function getParent()
    {
        return 'entity';
    }
}

config.yml

services:
    form.type.category:
        class: AcmeDemoBundle\Form\Type\CategoryType
        tags:
            - { name: form.type, alias: category }

fields.html.twig

{% block category_choice_widget_options %}
{% spaceless %}
{% for index, choice in options %}
{% if _form_is_choice_group(choice) %}
<optgroup label="{{ index|trans({}, translation_domain) }}">
    {% for nested_choice in choice %}
    <option value="{{ nested_choice.value }}"{% if _form_is_choice_selected(form, nested_choice) %} selected="selected"{% endif %}>{{ nested_choice.label|trans({}, translation_domain) }}</option>
    {% endfor %}
</optgroup>
{% else %}
<option {% if choice.label.isTopLevel %}class="isTopLevel"{% endif %} value="{{ choice.value }}"{% if _form_is_choice_selected(form, choice) %} selected="selected"{% endif %}>{{ choice.label.label|trans({}, translation_domain) }}</option>
{% endif %}
{% endfor %}
{% endspaceless %}
{% endblock category_choice_widget_options %}



{% block category_choice_widget_collapsed %}
{% spaceless %}
<select {{ block('widget_attributes') }}{% if multiple %} multiple="multiple"{% endif %}>
    {% if empty_value is not none %}
    <option value="">{{ empty_value|trans({}, translation_domain) }}</option>
    {% endif %}
    {% if preferred_choices|length > 0 %}
    {% set options = preferred_choices %}
    {{ block('choice_widget_options') }}
    {% if choices|length > 0 and separator is not none %}
    <option disabled="disabled">{{ separator }}</option>
    {% endif %}
    {% endif %}
    {% set options = choices %}
    {{ block('category_choice_widget_options') }}
</select>
{% endspaceless %}
{% endblock category_choice_widget_collapsed %}

{% block category_widget %}
{% spaceless %}
{% if expanded %}
<ul {{ block('widget_container_attributes') }}>
    {% for child in form %}
    <li>
        {{ form_widget(child) }}
        {{ form_label(child) }}
    </li>
    {% endfor %}
</ul>
{% else %}
{# just let the choice widget render the select tag #}
{{ block('category_choice_widget_collapsed') }}
{% endif %}
{% endspaceless %}
{% endblock %}

yourFormType.php

 $builder->add('category', 'category', array(
            'class' => 'AcmeDemoBundle:Category',
            'property' => 'CategoryTypeTitle'
        ));